The present invention generally relates to composite materials that are suitable for the protection of personnel and/or property from impact due to ballistic projectiles. Particular embodiments of the composite materials described herein comprise elastomeric materials for the reduction of trauma caused by impact with a ballistic projectile.
Stopping a ballistic projectile prior to entry into the body does not mean that a person will necessarily survive its impact. Even if a person is protected from injury caused by penetration from a ballistic projectile by wearing armor, the person may still be injured or killed due to the trauma inflicted by the ballistic projectile. The term “trauma” as used herein describes injuries caused by an impact on the body even in the absence of ballistic penetration. For example, broken bones, internal bleeding, and/or shock may commonly result from shooting incidents even if the wearer is protected from ballistic penetration by a bullet-proof vest or other protective garment.
The United States National Institute of Justice (NIJ) publishes a series of standards, particularly NIJ Standard-0101.04, to which protective garments, particularly protective or bullet-proof vests, are tested. The test protocols specify the type and velocity of the ballistic threat to be tested, the number and placement of shots, and the criteria for an acceptable test. The foregoing standards take into account trauma damage by measuring the depth of deflection of a backing material such as Roma Plastilina Number One clay created by a nonpenetrating projectile impact, which is referred to as backface signature or BFS. Complete penetration of the body armor or any designated depth measurement of BFS in the backing material of greater than 44 millimeter (mm) by any fair hit shall constitute a failure. The United Kingdom, which has a similar test for measuring BFS known as United Kingdom's Police Scientific Development Branch Stab-resistant Body Armour Test Procedure, considers depth measurements of BFS in the backing material of greater than 25 mm failures. Although no correlation between the BFS results of the NIJ test or UK test and specific injury to human subjects has been officially established, it is known that the overall reduction of trauma increases the likelihood of survival and reduces recovery time and medical costs. Therefore, an important element of survival is the dissipation of the impact shock-wave prior to its reaching the body.
Presently, armor manufacturers address trauma-reduction by typically requiring the utilization of a secondary soft armor pack to be worn behind the primary rigid-type or hard armor. These “trauma packs” as they are frequently termed, contain various layers of ballistic fabrics and foams. Their purpose is two-fold: capture any fragments or spall coming out the backside of the armor and attenuate the shock transmitted to the body of the person being protected. Although trauma packs have shown some success in decreasing the BFS profile of the primary armor by absorbing the energy of impact rather than transmitting it to the wearer, the need to have two layers of armor for protection adds weight and complexity to the final armor package. Trauma packs containing foam padding can typically be uncomfortably thick and trap excess heat and moisture close to the body. Confusion can also arise as to which secondary soft-armor packs have been certified for use with various primary hard-armor components. Thus, it can be seen that the need exists for improved and simplified materials and constructions for absorbing impact energy and reducing trauma to the body.
Elastomers, such as, for example, polyureas, polyurethanes and combinations or derivatives thereof, recently emerged as promising new materials that can accomplish at least one of the following: improve the multi-hit performance of ceramic armor, promote adherence or attachment of ceramic components to metal substrates, and/or protect against spall. Since elastomers can attenuate stress waves rapidly, it is believed that an innovative incorporation of elastomers to primary armor constructs could attenuate trauma and BFS of the primary armor constructs. For example, U.S. Pat. No. 6,532,857 describes the encapsulation of an array of ceramic tiles in an elastomer, typically a polysulfide, to improve the multi-hit performance of lightweight ceramic armor. Similarly, the application WO 2005/103363 A2 describes the encapsulation of either small ceramic inclusions or monolithic plates with a strain-rate hardening polyurea to improve the multi-hit capabilities of ceramic armor. Further, published application US 2007/0017359 A1 describes the using a plural-component spray polyurea as an adhesive to attach a multitude of ceramic spheres to an armor substrate for superior blast and ballistic mitigation.
In addition to trauma-reduction, the overall weight of the final armor package is also important. One of the more common materials used in primary armor is boron carbide ceramic tiles. While ceramic plates have an outstanding ballistic performance to weight ratio, the plates typically require some type of a wrap or coating due in part to its propensity to fracture under rough handling thereby decreasing their ballistic performance. One solution may be to have a coating applied directly to the ceramic plate. This may effectively mitigate trauma by providing protection against fracture while decreasing the overall weight of the armor package, since not as much secondary soft-armor may be needed to pass the NIJ standard trauma requirements.
Accordingly, there is a need in the art for improved materials for absorbing the impact of ballistic projectiles while decreasing the weight of, or eliminating the need for, secondary soft-armor. There is a further need in the art for cost effective methods of making these improved materials.